Input and Interstage Transformers

Author: N.H. Crowhurst

Input transformer matches low-impedance microphone to high-impedance vacuum tube input

Audio transformers are used where the impedance is not naturally what is needed for best performance. For low-impedance pickups or microphones working into tube grids, the transformer steps up the minute voltages (in this case impedance is incidental) to achieve better margin over tube noise. Sometimes interstage transformers are used for essentially the same purpose. The limit to what can be done occurs when the impedance connected to the primary is stepped up to such a value that it adversely affects performance in some other way.

Interstage transformers can be used to increase the effective gain of the amplifier